The intrinsic alignment of galaxy shapes with the large-scale density field is a contaminant to weak lensing measurements, as well as being an interesting signature of galaxy formation and evolution (albeit one that is difficult to predict theoretically). Here we investigate the shapes and relative orientations of the stars and dark matter of halos and subhalos (central and satellite) extracted from the MassiveBlack-II simulation, a state-of-the-art high resolution hydrodynamical cosmological simulation which includes stellar and AGN feedback in a volume of (100h −1 Mpc) 3 . We consider redshift evolution from z = 1 to 0.06 and mass evolution within the range of subhalo masses, 10 10 − 6.0 × 10 14.0 h −1 M . The shapes of the dark matter distributions are generally more round than the shapes defined by stellar matter. The projected root-mean-square (RMS) ellipticity per component for stellar matter is measured to be e rms = 0.28 at z = 0.3 for M subhalo > 10 12.0 h −1 M , which compares favourably with observational measurements. We find that the shapes of stellar and dark matter are more round for less massive subhalos and at lower redshifts. By directly measuring the relative orientation of the stellar matter and dark matter of subgroups, we find that, on average, the misalignment between the two components is larger for less massive subhalos. The mean misalignment angle varies from ∼ 30 • − 10 • for M ∼ 10 10 − 10 14 h −1 M and shows a weak dependence on redshift. We also compare the misalignment angles in central and satellite subhalos at fixed subhalo mass, and find that centrals are more misaligned than satellites. We present fitting formulae for the shapes of dark and stellar matter in subhalos and also the probability distributions of misalignment angles. 1 http://www.lsst.org/lsst/ and Euclid 2 aim to determine the constant and dynamical parameters of the dark energy equation of state to a very high precision using weak lensing.However, constraining cosmological parameters with sub-percent errors in future cosmological survey requires the systematic errors to be well below those in typical weak lensing measurements with current datasets. The intrinsic shapes and orientations of galaxies are not random but correlated with each other and the underlying density field. This is known as intrinsic galaxy alignments. The intrinsic alignment (IA) of galaxy shapes with the underlying density field is an important theoretical uncertainty that contaminates weak lensing measurements (Heavens et al. 2000; Croft 2 http://sci.esa.int/euclid/ c 0000 RAS arXiv:1403.4215v1 [astro-ph.CO]

The intrinsic alignment of galaxies with the large-scale density field is an important astrophysical contaminant in upcoming weak lensing surveys. We present detailed measurements of the galaxy intrinsic alignments and associated ellipticity-direction (ED) and projected shape (w g+ ) correlation functions for galaxies in the cosmological hydrodynamic MassiveBlack-II (MB-II) simulation. We carefully assess the effects on galaxy shapes, misalignment of the stellar component with the dark matter shape and two-point statistics of iterative weighted (by mass and luminosity) definitions of the (reduced and unreduced) inertia tensor. We find that iterative procedures must be adopted for a reliable measurement of the reduced tensor but that luminosity versus mass weighting has only negligible effects. Both ED and w g+ correlations increase in amplitude with subhalo mass (in the range of 10 10 − 6.0 × 10 14 h −1 M ), with a weak redshift dependence (from z = 1 to z = 0.06) at fixed mass. At z ∼ 0.3, we predict a w g+ that is in reasonable agreement with SDSS LRG measurements and that decreases in amplitude by a factor of ∼ 5-18 for galaxies in the LSST survey. We also compared the intrinsic alignments of centrals and satellites, with clear detection of satellite radial alignments within their host halos. Finally, we show that w g+ (using subhalos as tracers of density) and w δ+ (using dark matter density) predictions from the simulations agree with that of non-linear alignment models (NLA) at scales where the 2-halo term dominates in the correlations (and tabulate associated NLA fitting parameters). The 1-halo term induces a scale dependent bias at small scales which is not modeled in the NLA model.

We compare the shapes and intrinsic alignments of galaxies in the MassiveBlack-II cosmological hydrodynamic simulation (MBII) to those in a dark matter-only (DMO) simulation performed with the same volume (100h −1 Mpc) 3 , cosmological parameters, and initial conditions. Understanding the impact of baryonic physics on galaxy shapes and alignments and their relation to the dark matter distribution should prove useful to map the intrinsic alignments of galaxies from hydrodynamic to dark matter-only simulations. We find that dark matter subhalos are typically rounder in MBII, and the shapes of stellar matter in low mass galaxies are more misaligned with the shapes of the dark matter of the corresponding subhalos in the DMO simulation. At z = 0.06, the fractional difference in the mean misalignment angle between MBII and DMO simulations varies from ∼ 28% − 12% in the mass range 10 10.8 − 6.0 × 10 14 h −1 M . We study the dark matter halo shapes and alignments as a function of radius, and find that while galaxies in MBII are more aligned with the inner parts of their dark matter subhalos, there is no radial trend in their alignments with the corresponding subhalo in the DMO simulation. This result highlights the importance of baryonic physics in determining the alignment of the galaxy with respect to the inner parts of the halo. Finally, we compare the ellipticity-direction (ED) correlation for galaxies to that for dark matter halos, finding that it is suppressed on all scales by stellar-dark matter misalignment. In the projected shape-density correlation (w δ+ ), which includes ellipticity weighting, this effect is partially canceled by the higher mean ellipticities of the stellar component, but differences of order 30 − 40% remain on scales > 1 Mpc over a range of subhalo masses, with scale-dependent effects below 1 Mpc.

Whether among the myriad tiny proto-galaxies there exists a population with similarities to present day galaxies is an open question. We show, using BlueTides, the first hydrodynamic simulation large enough to resolve the relevant scales, that the first massive galaxies to form are predicted to have extensive rotationally-supported disks. Although their morphology resembles in some ways Milkyway types seen at much lower redshifts, these high-redshift galaxies are smaller, denser, and richer in gas than their low redshift counterparts. From a kinematic analysis of a statistical sample of 216 galaxies at redshift z = 8 − 10 we have found that disk galaxies make up 70% of the population of galaxies with stellar mass 10 10 M or greater. Cold Dark Matter cosmology therefore makes specific predictions for the population of large galaxies 500 million years after the Big Bang. We argue that wide-field satellite telescopes (e.g. WFIRST) will in the near future discover these first massive disk galaxies. The simplicity of their structure and formation history should make possible new tests of cosmology.

SPHEREx, the Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer, is a proposed NASA MIDEX mission selected for Phase A study pointing to a downselect in early CY2019, leading to launch in CY2023. SPHEREx would carry out the first all-sky spectral survey at wavelengths between 0.75 and 2.42 µm [with spectral resolution R=41], 2.42 and 3.82 µm [with R=35], 3.82 and 4.42 µm [with R=110], and 4.42 and 5.00 µm [with R=130]. At the end of its two-year mission, SPHEREx would obtain 0.75-to-5µm spectra of every 6.2×6.2 arcsec pixel on the sky, with a 5-sigma sensitivity AB>19 per spectral/spatial resolution element. SPHEREx would obtain spectra of every sources in the 2MASS PSC (1.2µm, 1.6µm, 2.2µm) catalog to at least (40 σ, 60 σ, 150 σ) per spectral channel, and spectra with S/N ≥3 per frequency element of the faintest sources detected by WISE. More details concerning SPHEREx are available at http://spherex.caltech.edu. The SPHEREx team has proposed three specific science investigations to be carried out with this unique data set: cosmic inflation, interstellar and circumstellar ices, and the extra-galactic background light.Though these three scientific issues are undoubtedly compelling, they are far from exhausting the scientific output of SPHEREx. Indeed, as Table 1 shows, SPHEREx would create a unique all-sky spectral database including spectra of very large numbers of astronomical and solar system targets, including both extended and diffuse sources. These spectra would enable a wide variety of scientific investigations, and the SPHEREx team is dedicated to making the SPHEREx data available to the scientific community to facilitate these investigations, which we refer to as Legacy Science. To that end, we have sponsored two workshops for the general scientific community to identify the most interesting Legacy Science themes and to ensure that the SPHEREx data products are responsive to their needs. In February of 2016, some 50 scientists from all scientific fields met in Pasadena to develop these themes and to understand their implications for the SPHEREx mission. The results of this initial workshop are reported in Doré et al., 2016. Among other things, discussions at the 2016 workshop highlighted many synergies between SPHEREx Legacy Science and other contemporaneous astronomical missions, facilities, and databases. Consequently, in January 2018 we convened a second workshop at the Center for Astrophysics in Cambridge to focus specifically on these synergies. This white paper, which contains substantial contributions from the participants, presents some of the highlights of the 2018 SPHEREx workshop. 1